The present invention concerns programmable, fully automatic shutter systems for photographic cameras, of the type in which the user is provided with at least some preselectability of exposure-aperture size or exposure duration, and cooperating with an electronic exposureduration control system of the type which activates, e.g., deenergizes, a holding electromagnet to permit the shutter to close at the moment when the totalized or integrated amount of light incident upon the camera's light sensor has reached a predetermined value. Also, shutter systems of the type in question are typically provided with means automatically operative for indicating to the user whether the prevailing scene-light level, i.e., taken in conjunction with further exposure parameters such as film sensitivity and the preselected shutter speed or aperture size, does or does not permit hand-held shooting or whether instead a tripod or flash illumination would be required.
The preferred embodiment of the invention, as explained much more fully below, makes use of an electromagnetic braking or retarding mechanism in conjunction with a shutter and a double diaphragm, one of the apertures of the double diaphragm being located in line with the shutter in the path of exposure light and the other aperture of the double diaphragm being located to control the incidence of light on the camera's light sensor. This basic approach results in a very considerable number of system flexibilities, which will be explained further below. However, inasmuch as electromagnetic braking or motion-retarding is involved, a brief discussion of the relevant prior-art aspects of such technique is in order.
In photographic cameras, braking or motion-retarding mechanisms are known, in a considerable variety of forms, for the purpose of controlling the speed of shutter movement and thereby exposure duration. For such purposes, it is also known in the prior art to make use of electromagnetic braking or motion-retarding systems. In general, these are so designed that the motion-retarding action is automatically controlled in dependence upon the light incident upon the camera's light sensor; e.g., the motion-retarding electromagnet, a current source, a photoresistor, and a control switch are connected in series, and variations in the level of light incident on the photoresistor result in corresponding variations of the motion-retarding action afforded by the electromagnet. The control switch is closed when the user depresses the camera release button, or other such user-activated member. Such a system is disclosed, by way of example, in published Federal Republic of Germany allowed patent application DT-AS No. 1,258,258.
Such shutter systems, i.e., wherein the control of shutter operation includes the use of an electromagnetic braking or motion-retarding force, can be designed in various ways from various viewpoints, for example depending upon the number of blades with which the shutter is provided, and depending upon what special functions or particular modifications of shutter performance the electromagnetic motion-retarding force is to be called upon to provide.
It is also known to use such electromagnetic motion-retarding systems, and to vary the intensity of their electromagnetic fields, for the purpose of controlling the distance through which the structure defining the exposure aperture moves, i.e., in order to determine or control exposure-aperture size. However, these known systems can only be used for pure and simple diaphragm-aperture regulation of the type which does not exhibit real functional dependence upon, or in particular complicated functional dependence, upon one or more further exposure parameters.
In view of such recognized flexibility limitations of shutter systems relying on magnetic-force motion retardation, attempts have been made to develop special-purpose motion-retarding and control systems specifically adapted for controlling the motions of mechanical components in photographic cameras, in which a permanent magnet connected to a moving component cooperates with one or more further, magnetically interconnected permanent magnets located along a motion-retarding path in such a manner that the particular motion-retarding function, e.g., the motion-retarding force as a function of displacement, or the like, is determined by the dimensions and configuration of a flux-return yoke cooperating with such permanent magnets; or else, the permanent magnet is provided with one or more specially configured shaped portions of cut-outs in its magnetic material whose configuration is then relied on to establish the particular motion-retarding function desired by the designer. However, even with that prior-art technique, the manner in which the motion-retarding function is generated, and the resulting exposure durations corresponding to such function, cannot be realized if the system is additionally to afford user-selectability of exposure duration and/or exposure-aperture size.